Basil
Sweet Basil, Thai Basil, Genovese Basil, Purple Basil, Lemon Basil, Basil
Extremely frost-sensitive; don't plant until night temps stay above 50°F. Pinch flower heads as soon as they appear to maintain leaf production. Harvest from the top, taking 1/3 at a time. Downy mildew is a major threat — choose resistant varieties (e.g., 'Amazel'). Water at base; avoid wetting foliage.
- Germination
- 5–10 days
- Soil temperature
- 18–29 °C
- Harvest after planting
- 60–90 days
- Spacing
- 30–45 cm
When to plant basil
Start seeds indoors 4–6 weeks before your last spring frost, and plant out 1–3 weeks after it.
Dashed line: typical last spring frost in zone 7 (Apr 5). Zone dates are averages; most of the UK is zone 8–9, central Europe 6–7 and the Baltics and Scandinavia 4–6. In the app, Tomatograph uses your garden's own frost dates.
How to grow basil
- 1
Sow indoors
Sow 6 mm deep 4–6 weeks before the last frost at 18–29 °C. Seedlings appear in 5–10 days.
- 2
Plant out late
Basil is very frost-sensitive. Plant out only once nights stay above 10 °C, or keep it in pots on a sunny sill.
- 3
Pinch and water
Pinch out flower buds as soon as they appear to keep leaves coming. Water at the base in the morning; wet leaves invite downy mildew.
- 4
Harvest
Pick from the top, taking no more than a third of the plant at once, from 60 days after planting. Cutting just above a pair of leaves makes it bushier.
Growing conditions
Light
Full sun
Water
Medium water
Temperature
15–35 °C
Frost tolerance
Frost-sensitive — protect below 0 °C
Days to maturity
60 days
Plant spacing
30 cm
Ideal soil pH
6.5–7
How Tomatograph watches your basil
Tomatograph checks your local forecast every morning and only speaks up when one of these applies to your garden.
- Forecast of 2 °C or lowerFrost alert the evening before: cover plants with fleece or bring pots inside.
- 3 days at 35 °C or aboveHeat-wave alert while plants are flowering or fruiting: shade and water early.
- Humidity above 80% for 48 hoursCheck for downy mildew, which thrives in those conditions.
- Within a week of maturityHarvest-window reminder based on when you planted.
Basil questions
- When should I plant basil?
- Start seeds indoors 4–6 weeks before your last spring frost, and plant out 1–3 weeks after it.
- How long do basil seeds take to germinate?
- Usually 5–10 days at a soil temperature of 18–29 °C.
- How long until I can harvest basil?
- About 60–90 days after planting out, depending on variety and weather.
- How far apart should I plant basil?
- Allow 30–45 cm between plants.
- What grows well with basil?
- Good neighbours include tomato, pepper, lettuce.
Growing guide written by Tomatograph. Planting figures from openplantdb (CC0 1.0). Zone frost dates are averages from openplantdb (CC0 1.0).